Soil development along an elevational transect in the western Sierra Nevada, California

Soil development along an elevational transect on the western slopes of the central Sierra Nevada was investigated to assess the effects of climate on soil properties and processes, The transect of seven soils formed in granitic residuum spans elevations from 198 to 2865 m with mean annual temperature and precipitation differences of 13 degrees C (3.9-16.7) and 94 cm (33-127), respectively. Soil pH decreased by about two units and base saturation decreased from 90 to 10% with increasing elevation. Concentrations of organic C in the solum increased with elevation, with the largest single increase occurring between the oak woodland (5-6 kg C/m(2)) and mixed-conifer sites (10-15 kg C/m(2)). Clay mineralogy showed a general trend of desilication and hydroxy-Al interlayering of 2:1 layer silicates with increasing elevation, The degree of chemical weathering, based on clay and secondary Fe oxide concentrations in the solum, showed a maximum (clay = 536 kg/m(2) and Fe oxides = 24 kg/m(2)) at mid-elevations having intermediate levels of precipitation and temperature. While some soil properties show a continuous progression (e.g., organic carbon, base saturation, clay mineralogy) with elevation, other properties (e.g., pH, soil color, clay and secondary Fe oxide concentrations) show a pronounced change (threshold-type step) over a short distance at about 1600 m. The explanation for the abrupt nature of this shift is not known; however, it coincides with the approximate elevation of the present-day average effective winter snow-line. (C) 1997 Elsevier Science B.V.